1. Field
The present invention relates to a washing machine, and more particularly, to a washing machine having a water softening device.
2. Description of the Related Art
In general, water, and particularly underground water, contains a large quantity of minerals such as calcium, magnesium, etc. A numerical value obtained by digitizing the total amount of calcium, magnesium, etc. is referred to as hardness. Water having a high hardness is referred to as hard water, and water having a low hardness is referred to as soft water.
When tea is made using hard water, i.e., water having a high hardness, the tea tastes bitter. Further, when hard water flows in a pipe, the hard water generates scale on the inner surface of the pipe and thus reduces heat transfer performance and flow characteristics of a fluid. In the case that the scale is not removed periodically, the pipe may be broken.
Further, in the case that hard water is used in a washing machine, the hard water reacts with soap and thus lowers detergency, and in the case that hard water is used in a steam generating unit or a heater in a washing machine, the hard water generates scale and thus lowers energy efficiency and causes clogging of a nozzle.
That is, when hard water is used in a washing machine using water, washing power is lowered and a large quantity of scale is accumulated on a channel passing water, and thus the reliability of a washing machine product is lowered.
In order to solve the above problem, a washing machine having a water softening device using ion exchange resin and a washing machine having a water softening device using capacitive deionization have been proposed.
A water softening method using ion exchange resin is that water is softened by exchanging Ca2+ and Mg2+ ions, i.e., hard water components, contained in water, with Na+ ions of NaCl implanted in the ion exchange resin. A water softening device using the above ion exchange resin has a large volume, and thus it is difficult to install the water softening device in a compact-sized washing machine. Further, this water softening device requires periodic NaCl implantation, and replacement of the ion exchange resin with a new one due to impurities contained in water, thus increasing expenses.
In order to solve the above problem of the water softening method using ion exchange resin, Korean Utility Model Publication No. 1990-0005239 discloses an apparatus for manufacturing magnetized water, which softens water by magnetization treatment.
The above apparatus for manufacturing magnetized water, disclosed in the above Korean Utility Model, includes a magnetic field forming unit having magnets having a rectangular or circular-shaped cross section separated outwardly from the outer circumference of a pipe, in which natural water flows, at a regular interval, and a horseshoe magnet closely fixed to the magnets, such that the natural water flowing in the pipe at a regular current speed is magnetized by a magnetic field generated by the magnetic field forming unit.
However, since the magnetic field forming unit is provided at the outside of the pipe, the magnetic flux of the magnetic field forming unit cannot be concentrated on water to be softened. Thus, the above-disclosed apparatus for manufacturing magnetized water has a low water softening efficiency.
Further, since the pipe is configured such that the natural water flows in the pipe at a regular current speed, the flux state of the natural water flowing in the pipe is stabilized and the natural water cannot be sufficiently magnetized by the magnetic field formed by the magnetic field forming unit. Thus, the above-disclosed apparatus for manufacturing magnetized water has a low water softening performance.
Capacitive deionization (hereinafter, referred to as “CDI”) is a regenerating operation that is performed by applying a proper voltage to a plurality of porous electrodes and causing water containing ions to flow between the porous electrodes such that positive ions are attracted to a cathode and negative ions are attracted to an anode so as to remove ion components from a medium, and then by applying opposite voltages to the electrodes saturated with the positive and negative ions or short-circuiting the electrodes so as to separate the ions from the electrodes. Korean Patent Laid-open Publication No. 2000-000060149 discloses a washing machine having a water softening device using CDI.
The above water softening device using CDI is expensive and has a relatively small amount of water to be treated, compared with the water softening device using ion exchange resin, thus being ineffective in a washing machine requiring rapid supply of a large amount of water.
Washing machines having the above-described water softening devices soften water supplied from a water supply source and then mix the obtained soft water with a detergent, and supply the water mixed with the detergent to a tub, thus lowering a water softening performance. Further, these washing machines have a water supply time longer than a detergent supply time, and cause the water to be mixed with the detergent supplied from a detergent supply unit and then to be supplied directly to the tub without dissolving the detergent in the water, thus lowering the solubility of the detergent.